The CCR5 chemokine receptor is known to act as a coreceptor in conjunction with CD4 for the entry of macrophage tropic nonsyncytia-inducing (NSI) strains of HIV-1 during infection. The NSI, or macrophage tropic, strains are apparently the most prevalent strains in HIV positive individuals. Recent studies have indicated that the CCR5 genotype is important in predicting host susceptibility to HIV-1 infection as well as determining disease progression.
A 32 base deletion mutation in the CCR5 gene has been found to occur in some individuals. Individuals who are homozygous for this deletion mutation do not express the CCR5 receptor on the surface of their CD4+ cells and appear not to be injectable by NSI isolates of HIV-1. Individuals who are heterozygous for this deletion mutation, i.e., have a wild type (wt) CCR5 allele and a mutant (mut) CCR5 allele, appear to be injectable, but disease progression is less rapid and less severe than that of individuals who are homozygous for the wild type allele.
In view of the apparent relationship of the CCR5 genotype to HIV-1 infection and progression, an assay method that can determine whether an individual is homozygous mutant, heterozygous, or homozygous wild type at the CCR5 gene can serve as a diagnostic marker for (1) infectability by NSI forms of HIV-1 and (2) disease progression prognoss.